linux-kernel - Re: [BUG] perf: perf sched warning possibly due to clock granularity on AMD

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Date:	Wed, 8 Feb 2012 16:23:37 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com,
	peterz@...radead.org, mingo@...e.hu, robert.richter@....com,
	eric.dumazet@...il.com
Subject: Re: [BUG] perf: perf sched warning possibly due to clock granularity
 on AMD

On Wed, Feb 8, 2012 at 4:22 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> On Wed, Feb 08, 2012 at 04:10:24PM +0100, Stephane Eranian wrote:
>> On Wed, Feb 8, 2012 at 4:07 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
>> > On Mon, Feb 06, 2012 at 02:25:46PM +0100, Stephane Eranian wrote:
>> >> Hi,
>> >>
>> >> I am running 3.3.30-rc2 on an AMD Bulldozer system in 64-bit mode.
>> >> I was testing perf sched and I ran into an issue. That issue seems
>> >> to exist only on AMD and not on Intel systems. It is not PMU related
>> >> because I am doing tracing.
>> >>
>> >> I am running a simple ping pong test to stress the context switch
>> >> code. Two processes exchanging a byte through a pipe (program provided
>> >> below).
>> >>
>> >> Then, I capture a trace using perf sched, and I run sched lat, but
>> >> on certain runs, I get:
>> >>
>> >>    $ perf sched rec pong 2
>> >>    $ perf sched lat
>> >>      Warning: Timestamp below last timeslice flush
>> >>      Warning: Timestamp below last timeslice flush
>> >>      Warning: Timestamp below last timeslice flush
>> >>      Warning: Timestamp below last timeslice flush
>> >>      Warning: Timestamp below last timeslice flush
>> >>      Warning: Timestamp below last timeslice flush
>> >>      Warning: Timestamp below last timeslice flush
>> >>      Warning: Timestamp below last timeslice flush
>> >>      Warning: TimesFound 4934 unknown events!
>> >>      Is this an older tool processing a perf.data file generated by a more recent tool?
>> >
>> > I've tried to reproduce this on an AMD phenom but haven't got any such
>> > warning.
>> >
>> It does not happen at each run.
>
> Yeah I tried 5 times but wasn't lucky.

That's not enough!

>
>>
>> > Is there any chance you could "perf archive" your data and upload it somewhere
>> > I can fetch it from?
>> >
>> I can send you the perf.data in a private Email.
>
> Thanks!

Will dig it up and send it to you.
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